Previously publications have disclosed the ability of an ION Sensitive Field Effect Transistor (ISFET) to detect chemicals proximate the sensing surface. This may be used to determine the presence of a target analyte by detection of products of a chemical reaction. In one example, ISFETs can be used determine the identity of one or more portions of a nucleic acid template by detecting the change in pH resulting from nucleotide insertion at the end of a nucleic acid. Typically hydrogen ions (protons) are released during the reaction. The electrical signal strength of the ISFET depends on the amount of hydrogen ions released, which is expressed as an analogue output signal, which is either a voltage or current signal.
For large scale arrays of ISFETs, such as might be used in DNA sequencing, the inventors have appreciated that processing this analogue data requires enormous computing power and a bandwidth of gigabits/second.
In addition, the normal method requires accurate analogue readout circuitry, and is sensitive to the parasitic components, and environmental electrical noise. High accuracy and large-scale analogue systems limit the processing speed and integration ability; thereby constraining the detection efficiency and scalability. Moreover, high performance front-end interface circuitry consumes large amounts of system area and power, make on-chip data processing unrealistic.
The inventors propose herein a novel semiconductor and method that addresses one or more of the above deficiencies.